Well, you said you don't have a problem with campers and U4e is not a camper-mod...
...I don't really get why you worry then?!?
I never had a problem with someone camping. I mean if you can't handle a camper it is YOUR problem not the problem of the game. U4e even has a lot of weapons which campers may like, but all of them are pretty nice useable against them.
And I don't see why the buying system is a pro-camping game. As you said: You miss some weapons in the standard maps to fight campers. With a buying system you can buy EVERY weapon. So if someone camps and you do not get along with that, you can simply conform yourself to his "style of fighting" and buy the fitting contra-weapon. There is ALWAYS a weapon for that in the laaaaaaarge U4e weaponry...